The present invention relates to mechanisms for determining relative angular position between two coaxially-related elements; more particularly, to mechanisms for continuously determining the instantaneous angular relationship between a camshaft pulley and a camshaft in a cam phaser apparatus for an internal combustion engine; and most particularly, to apparatus for making such instantaneous determination without contact between the two coaxially-related elements.
In apparatus including first and second elements having coaxial relative rotation therebetween about a mean angular position, the need arises to determine changes in the relative angular position in either direction. An especially demanding application is one in which both elements are being simultaneously rotated on a common shaft. Just such a situation occurs in variable cam phasing systems for internal combustion engines. The angular relationship between the camshaft pulley and the camshaft itself is variable and must be determined at all times, but conveying a signal from the rotating apparatus via prior art means is difficult and cumbersome.
One known approach is to use a conventional position sensor, resistive or otherwise, mounted on the rotating cam phaser, and to convey a signal to an engine control module (ECM) via slip rings. This solution is expensive to implement and is prone to failure.
Another known approach is to use digital Hall-effect proximity sensors to detect the passing of timing features on each of the elements. By measuring the time interval therebetween, the angular relationship can be inferred. This solution, while theoretically sound, is complicated to implement because the angular velocity of the engine can vary within a single revolution of the cam phaser, causing an error in the apparent time phase measurement.
What is needed is a simple, inexpensive, and reliable means for determining the phase relationship of first and second coaxially mounted rotatable elements in an assembly, especially a cam phaser.
It is a principal object of the present invention to provide a simplified and reliable measurement of the phase relationship of such elements.
It is a still further object of the invention to provide such measurement proximately and without electrical connection to the assembly.
Briefly described, apparatus in accordance with the invention includes a Hall-effect magnetic field strength sensor disposed coaxially adjacent to an assembly having first and second coaxially-related elements oscillatingly-rotatable about a mean angular relationship therebetween. One of the elements is provided with a threaded axial bore or stud, and the other of the elements is provided with a longitudinally-splined axial bore. A pin having threads on a first end and splines on the second end is matingly disposed on both the threads and splines, respectively, of the two coaxially-related elements. A permanent magnet is mounted on an end of the pin adjacent the Hall-effect sensor, creating a magnetic response therein. As the angular relationship between the two elements changes, the pin turns with the splined element. However, the turning pin is simultaneously displaced axially of the assembly by the threads, thus displacing the magnet with respect to the sensor and thereby changing the intensity of the field experienced by the sensor. Thus, the sensor output is a continuous signal representing the intensity of magnetic field which is directly proportional to the relative angular position of the two elements. Because the magnet and sensor are coaxially disposed, rotation of the magnet, as occurs, for example, in a cam phaser application, is irrelevant. In such an application, the sensor signal is provided to an engine control module for continuous monitoring and control of the advance and retard timing of engine intake valve opening and closing.